X-ray apparatus for generating short x-ray pulses, and inspecting device operating by means of such an x-ray apparatus

ABSTRACT

An invention related to an X-ray device for the generation of brief X-ray pulses comprising an X-ray tube having a thermionic cathode and an anode and an X-ray generator having a first circuit for the generation of a high-voltage pulse which is applied to the anode for the generation of the X-ray pulse. The X-ray generator further comprising a second circuit by which a low voltage is continuously applied to the anode which pre-heats the X-ray tube and is at most sufficient for the generation of low-energy X-radiation. The first circuit can have a high-voltage power supply unit which charges a high-voltage capacitor which can be applied to the anode via a high-voltage switch. The first circuit can be a Marx generator. There may be only one power supply, which both generates the continuously low voltage and also drives the Marx generator for the generation of the high voltage. The X-ray unit can be part of an apparatus for the inspection of objects which has an imaging apparatus for the generation of an image of the object by means of the X-ray.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application claims priority from patent applicationPCT/EP2003/013082 filed Nov. 21, 2003, which claims priority from GermanPatent Application Number 202 18 138.3, which was filed on Nov. 21,2002, the entire content of which is herein incorporated by reference.

FIELD OF THE INVENTION

This invention relates to the inspection of objects, especiallycontainers.

BACKGROUND OF THE INVENTION

It is known to use X-rays to inspect drink bottles and luggage which aremoved past an imaging apparatus onto a transport device. X-ray imageintensifiers or converters with a downstream CCD camera are used asimaging systems and the recorded image relayed to an evaluation system.By using a surface sensor in the X-ray image intensifier it is possibleto greatly reduce both the radiation energy and also the power input ofthe X-ray pulse. However, due to the movement of the X-rayed objects,the contours of the images lack sharpness.

If other sensors are used, e.g. line sensors such as a plurality ofphotomultiplier tubes arranged in a row with the scintillator crystals,all of the energy must be made available continuously even when noobject is in the beam path to be inspected. As a result, high radiationenergies are released, and high electric outputs are required. Expensivescreening and security measures are therefore required for the highconnected loads of the equipment and radiation protection.

X-ray units for the generation of brief X-ray pulses are known fromDE-C-32 16 733, U.S. Pat. No. 4,947,415 and WO 94/23552. These unitsserve to generate extremely brief X-ray pulses lasting a fewnanoseconds. Specially developed capacitors are used to generate thehigh-voltage pulse, in order to be able to transmit the high-voltageenergy to the anode within an extremely brief pulse duration.

An X-ray unit with an electron field emission cathode is known from WO02/31857, with which X-ray pulses of different energies can be generatedby focusing the electron beam on different anode materials.

An X-ray beam generator for the generation of X-ray pulses is known fromEP-A-1 158 842, the high voltage being applied continuously to the anodeand the grid voltage being controlled according to the cathode currentsuch that during the period in which no X-ray beams are to be generated,no electrons reach the anode. The pulse duration is also controlled bymeans of the grid voltage. It is thereby made possible to generate astable X-ray pulse.

BRIEF SUMMARY OF THE INVENTION

The invention is directed to an X-ray unit for the generation of X-raypulses in the millisecond range. According to the invention this objectis achieved by an X-ray unit comprising an X-ray tube with a thermioniccathode, an anode, and an X-ray generator that generates a high-voltagepulse and continuously applies low voltage to the anode of the X-raytube.

The invention is also directed to an apparatus for inspecting objects.In one embodiment, the apparatus comprises the X-ray unit describedabove and an imaging apparatus for generating an image of an object withan X-ray. The X-ray unit is particularly suitable for use in anapparatus for the inspection of objects, such as containers, drinkbottles, suitcases etc., transported through the apparatus at irregularintervals because the start phase for powering-up the X-ray tube isextremely brief. The start phase is essentially defined only by thedischarge curve of the capacitors thus making possible contour-sharpimages with relatively low radiation energy. This is an advantage overthe prior art because it provides sharp images with reduced radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an embodiment of the X-ray device.

FIG. 2 is a circuit diagram of an embodiment of a Marx generator.

FIG. 3 is a front view of one embodiment of an apparatus according tothe invention wherein the X-ray device represented in FIG. 1 is used toinspect drink bottles.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1-3, the invention is directed to a device for thegeneration of brief X-ray pulses and also to an apparatus for theinspection of objects such as containers, drink bottles, suitcasesetcetera. The X-ray unit contains an X-ray tube with a thermioniccathode and an anode, and it also contains an X-ray generator. The X-raygenerator has a first circuit for the generation of a high-voltage pulsewhich can be applied to the anode to generate the X-ray pulse.

The X-ray tube operates in simmer mode. The X-ray generator has a secondcircuit, a simmer power supply unit, which applies low voltage to theanode. By “low voltage” what is meant is a voltage at which at thelowest-energy X-radiation is generated that is absorbed by the glasswall of the X-ray tube. This low voltage is continuously applied to theanode, yet practically no X-radiation is generated. Nevertheless, theX-ray tube is pre-heated so that the X-ray tube can be quicklypowered-up at any time and a brief X-ray pulse generated.

A protective diode protects the simmer power supply unit when the highvoltage is switched on. Another possibility for the generation of thehigh-voltage pulse is the use of a Marx generator. The cathode is alwaysheated with constant heating current via a heating control.

Such an X-ray unit is particularly suitable as part of an apparatus forthe inspection of objects, in particular containers which aretransported through the inspection apparatus at irregular intervals.Because the start phase for powering-up the X-ray tube is extremelybrief and essentially is defined only by the discharge curve of thecapacitors, contour-sharp images are possible with relatively lowradiation energy.

The X-ray unit according to the invention is suitable in particular asan X-ray beam source in the case of the device in the utility modelapplication DE-U-202 17 559.6 (application date: 12^(th) Nov. 2002,title: “Device for testing filled containers using X-rays”).

Both the X-ray unit for the generation of brief X-ray pulses and theapparatus for the inspection of containers will now be described indetail with reference to the FIGS. 1-3.

In an embodiment as shown in the circuit diagram of FIG. 1, the cathode12 of an X-ray tube 10 is connected to a heating control 14. Thisprovides the cathode 12 with a constant heating current. Anode 16 isconnected via a high-voltage switch 18 to a high-voltage capacitor 20which is charged by a high-voltage power supply unit 22. Anode 16 isalso connected to a simmer power supply unit 26 via a protective diode24.

The high-voltage power supply unit 22 charges the high-voltage capacitor20 to 60 kV. By closing the high-voltage switch 18 this voltage isapplied to anode 16 of X-ray tube 10, whereby an X-ray 30 is generated.

The X-ray tube 10 is operated in simmer mode by a simmer power supplyunit 26, the simmer power supply unit 26 producing a voltage ofapproximately 5 kV and continuously allowing a direct current of betweenapproximately 1 to 10 mA to flow through the X-ray tube 10. The X-raytube 10 is thereby pre-heated to the point where it immediately powersup and generates an X-ray 30 as soon as the high-voltage switch 18 isclosed. The simmer power supply unit 26 is protected against the highvoltage of the capacitor 20 by the protective diode 24.

In another embodiment, instead of the high-voltage power supply 22 andthe high-voltage capacitor 20 and the high-voltage switch 18, a Marxgenerator can be used as shown in FIG. 2. The Marx generator is avoltage multiplier with which a pulsed high voltage can be generated. Anumber of n capacitors 33 which are connected in parallel by resistors34 are charged by a voltage source 32. To trigger the high-voltagepulse, the capacitors 33 are connected in series by an electronic switch36. Then the n-fold capacitor voltage is applied to the output 38.

If, for example, a voltage source 32 of 5 kV and 12 parallel-connectedcapacitors 33 are used, the generated high-voltage pulse is 60 kV.Therefore, in the present case the simmer power supply unit 26 can beused as voltage source 32.

FIG. 3 shows one embodiment of an apparatus for the inspection ofcontainers comprised of the X-ray unit described above and an imagingapparatus for generating an image of an object with an X-ray. In thisembodiment, drink bottles 40 are conveyed on a transport device 42 suchas a link chain conveyor. On one side of the transport device 42 thereis an X-ray tube 10. On the opposite side of the transport device 42,there is an X-ray image converter 44 behind which a CCD camera 46 isarranged. A trigger signal is generated by means of a device such as alight barrier or a capacitive sensor if a drink bottle 40 to beinspected is located between the X-ray tube 10 and the X-ray imageconverter 44. The high-voltage switch 18 is closed by the triggersignal, so that the X-ray tube 10 generates a pulse-like X-ray 30. Afterpassing through the bottle 40, the X-ray 30 strikes the X-ray imageconverter 44 and generates there an image of the drink bottle 40. Theimage is recorded by the CCD camera 46 and processed in known manner byimage-recognition processes in order to recognize foreign bodies, e.g.glass splinters, in the filled drink bottle 40. In order that any glasssplinters are not masked by the bulge at the bottom of the drink bottle40 the X-ray tube 10 is arranged above the plane of the transport device42 and directs the X-ray 30 at an angle of e.g. 30° from above onto thecontainer bottom, as is described in detail in the above-named utilitymodel application DE-U-202 17 559.6 (title: “Device for testing filledcontainers using X-rays”).

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention. Itshould be understood that the illustrated embodiments are exemplaryonly, and should not be taken as limiting the scope of the invention.

1. An X-ray device for the generation of at least one X-ray pulse, thedevice comprising: an X-ray tube having a thermionic cathode and ananode; and an X-ray generator comprising a Marx generator for thegeneration of at least one high-voltage pulse applied to the anode forthe generation of the at least one X-ray pulse, and a simmer powersupply unit by which a low voltage is continuously applied to the anodewherein the low voltage is at most is sufficient for the generation oflow-energy X-radiation and pre-heats the X-ray tube; wherein the simmerpower supply unit a voltage source of the Marx generator.
 2. Anapparatus for the inspection of objects, the apparatus comprising: anX-ray tube having a thermionic cathode and an anode: an X-ray generatorcomprising a Marx generator for generating at least one high-voltagepulse applied to the anode for the generation of at least one X-raypulse, and a simmer power supply unit by which a low voltage iscontinuously applied to the anode, wherein the low voltage pre-heats theX-ray tube and is at most sufficient for the generation of low-energyX-radiation; and an imaging apparatus for generating an image of theobject by means of the at least one X-ray pulse. 3-5. (canceled)
 4. Amethod of generating an X-ray pulse comprising: providing an X-ray tubehaving a thermionic cathode and an anode; preheating the X-ray tube bycontinuously applying a low voltage to the X-ray tube wherein the lowvoltage preheats the X-ray tube and is at most sufficient for thegeneration of low-energy X-radiation; generating at least one highvoltage pulse, and applying the at least one high voltage pulse to theanode to generate at least one X-ray pulse.
 5. The method of claim 4wherein the at least one high voltage pulse is generated by a Marxgenerator.
 6. The method of claim 4 wherein, a first circuit generatesthe at least one high voltage pulse, and wherein further, the X-ray tubeis preheated by a second circuit that is the voltage source of the firstcircuit.
 7. A method of inspecting objects comprising: providing anX-ray tube having a thermionic cathode and an anode; preheating theX-ray tube by continuously applying a low voltage to the X-ray tubewherein the low voltage preheats the X-ray tube and is at mostsufficient for the generation of low-energy X-radiation; generating atleast one high voltage pulse; applying the at least one high voltagepulse to the anode whereby at least one X-ray pulse is generated.passing the at least one X-ray pulse through an object; and generatingan image based on the at least one X-ray pulse passing thru the object.8. The method of claim 7 wherein the at least one high voltage pulse isgenerated by a Marx generator.
 9. The method of claim 7 wherein, a firstcircuit generates the at least one high voltage pulse, and whereinfurther, the X-ray tube is preheated by a second circuit that is thevoltage source of the first circuit.
 10. The method of claim 7 furthercomprising: transporting the object on a substantially horizontal planeof transport; and moving the object through the at least one X-ray pulsewherein the X-ray pulse has a predetermined direction.
 11. The method ofclaim 7, wherein the object is one of a plurality of containers beingtransported individually in succession in a row on a substantiallyhorizontal plane of transport.
 12. The method of claim 7, wherein the atleast one X-ray pulse passing through the object, strikes an X-ray imageconverter and generates an image therein that is recorded by a digitalcamera.